The present invention relates to a process and an apparatus for removing scales and preventing scale formation on hot rolled or heat-treated metallic materials or hot metallic materials, such as steel, iron alloys, copper, copper alloys, zinc, zinc alloys, aluminium, aluminium alloys on the like materials in such circumstances as to form oxide scales as in a hot rolling step and/or a cold rolling step or a heat-treating step following the continuous casting step, or a hot metallic material cooling step following these steps or in a pickling step as well, whereby suppression and removal of scales can be carried out efficiently at a low cost for a short time.
Metallic materials, particularly steel materials, react with atmospheric oxygen in a heating step and a rolling step or a hot steel material cooling step to form iron oxide called scales on the surfaces. The scales formed on the surfaces of steel materials are partly peeled off during the press working, etc. and pressed into products, sometimes thereby degrading the product quality, for example, flaw formation, etc. On the other hand, to prevent the quality degradation, a pickling step to wash off the scales with an aqueous hydrochloric acid solution, etc. has been additionally required.
Thus, processes for controlling oxidation on the steel material surfaces, thereby preventing scale formation have been so far proposed.
For example, a process for suppressing scale formation by applying an oxidation-suppressing agent to steel material surfaces to form a film is popular, but water, when contained in the oxidation-suppressing agent, boils at a temperature of 500xc2x0 C. or higher on the steel material surfaces and a water vapor layer is formed on the steel material surfaces, causing a failure to form an oxidation-suppressing agent film on the steel material surfaces or a failure of even application of the oxidation-suppresing agent. That is, there is such a disadvantage or a failure of full control of scale formation.
To overcome such a disadvantage, for example, Japanese Patent Koaki (Laid-Open) No. 4-236714 publication proposes a process for preventing scale formation on the steel material surfaces by applying to or spraying onto hot steel materials a polymer solution comprising copolymers containing ethylene oxide and propylene oxide as monomer components, which can be separated into liquid polymers and water when the solution reaches a temperature of 100xc2x0 C. or higher and can form an aqueous polymer solution at a temperature below 100xc2x0 C. upon mixing with water, but the pickling treatment still needs a long time.
The process for suppressing oxidation of steel materials disclosed in said Japanese Patent Kokai (Laid-Open) No. 4-236714 publication cannot remove such scales as formed before the application of the polymer solution. Even by applying the such a polymer solution thereto, scale formation is inevitable, though in a very small amount, ultimately requiring a pickling step to wash off such scales.
An object of the present invention is to overcome the problems of prior art and provide a process and an apparatus for removing scales and preventing scale formation on metallic materials in a hot rolling step and/or a heat treatment step, etc., which can conduct suppression and removal of scales efficiently and can largely shorten the treatment time in the successive pickling step.
Gists of the present invention are as follows:
(1) A process for removing scales and preventing scale formation on a metallic material, characterized by contacting cooling water with a metallic material at a temperature of 100xc2x0 to 1,200xc2x0 C. in a water cooling step for the metallic material, while applying a direct current or an alternating current to the metallic material at a current density of 0.1 to 105 A/m2 of unit surface area through the cooling water.
(2) A process for removing scales and preventing scale formation on a metallic material, characterized by contacting cooling water at a pH of xe2x88x922 to 4 with a metallic material at a temperature of 100xc2x0 to 1,200xc2x0 C. in a water cooling step for the metallic material.
(3) A process for removing scales and preventing scale formation on a metallic material, characterized by contacting cooling water at a pH of xe2x88x922 to 4 with a metallic material at a temperature of 100xc2x0 to 1,200xc2x0 C. in a water cooling step for the metallic material, while applying a direct current or an alternating current to the metallic material at a current density of 0.1 to 105 A/cm2 of unit surface area through the cooling water.
(4) A process for removing scales and preventing scale formation on a metallic material according to the foregoing item (1) or (3), characterized by using the metallic material as one of a positive electrode or a negative electrode or providing the metallic material between a positive electrode and a negative electrode for the current application.
(5) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1), (3) and (4), characterized by providing at least two of pairs each consisting of a positive electrode and a negative electrode facing each other discretely in a water cooling tank filled with cooling water so that the positive electrodes and the negative electrodes can be alternately arranged in a parallel with one another at distances, passing the metallic material through between the positive electrodes and the negative electrodes in the pairs in the cooling water, thereby contacting the cooling water with the metallic material, and applying a direct current to the metallic material by passing the current between the positive electrodes and the negative electrodes in the pairs.
(6) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) and (3) to (5), characterized in that the cooling water has an electric conductivity of 0.01 to 100 S/m.
(7) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (6), characterized in that water deaerated to a dissolved oxygen gas concentration of not more than 4.46xc3x9710xe2x88x925 mol/m3 (1 ppm) is used as the cooling water.
(8) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (7), characterized in that high pressure water with the pressure of 0.2942 to 49.03 MPa is made to hit the metallic material during the water cooling.
(9) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (8), characterized in that high pressure water with the pressure of 0.2942 to 49.03 MPa is made to hit the metallic material after the water cooling.
(10) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (9), characterized in that water containing at least one of hydrogen, ammonia, nitrogen, carbon dioxide and inert gases at a total dissolved gas concentration of 4.46xc3x9710xe2x88x925 mol/m3 to 2.23 mol/m3 (1 to 5xc3x97104 ppm) is used as the cooling water.
(11) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (2) to (10), characterized in that hydrochloric acid, sulfuric acid or nitric acid is added to the cooling water.
(12) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (2) to (10), characterized in that an oxidizing agent is added to the cooling water, thereby adjusting the cooling water to an ORP (oxidation-reduction potential) value of 0.5 V in NHE (Normal Hydrogen Electrode) to 2.0 V in NHE, or a reducing agent is added to the cooling water, thereby adjusting the cooling water to an ORP value of 0.5 V in NHE to xe2x88x921.5 V in NHE.
(13) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (2) to (10), characterized in that cooling water adjusted to an ORP (oxidation-reduction potential) value of 0.5 V in NHE to 2.0 V in NHE by an oxidizing agent or cooling water adjusted to an ORP value of 0.5 V NHE to xe2x88x921.5 V in NHE by a reducing agent are used alternately for the cooling.
(14) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (2) to (10), characterized in that oxidation potential water is partly or wholly used for the cooling water.
(15) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (14), characterized in that the cooling water is adjusted to a temperature of 50xc2x0 to 100xc2x0 C.
(16) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (15), characterized in that the cooling water is contacted with the metallic material at a relative speed of the cooling water and the metallic material to each other of 0.1 to 300 m/s.
(17) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (1) to (16), characterized in that the cooled metallic material is successively washed with a liquid and/or a gas and then coated with beef tallow, mineral oil or chemical synthesis oil, followed by coiling.
(18) A process for removing scales and preventing scale formation on a metallic material according to the foregoing item (17), characterized in that the beef tallow, mineral oil or chemical synthesis oil each contains 0.0001 to 1% by weight of boron.
(19) A process for removing scales and preventing scale formation on a metallic material, characterized by subjecting a metallic material heated to a temperature of 100xc2x0 to 700xc2x0 C. beforehand or a metallic material at a temperature of 100xc2x0 to 700xc2x0 C. from the beginning to a pickling treatment by a pickling solution at a pH value of xe2x88x922 to 4.
(20) A process for removing scales and preventing scale formation on a metallic material, characterized by subjecting a metallic material heated to a temperature of 100xc2x0 to 700xc2x0 C. beforehand or a metallic material at a temperature of 100xc2x0 to 700xc2x0 C. from the beginning to a pickling treatment by a pickling solution at a pH value of xe2x88x922 to 4, while applying a direct current or an alternating current thereto.
(21) A process for removing scales and preventing scale formation on a metallic material according to the foregoing item (20), characterized by providing at least two of pairs each consisting of a positive electrode and a negative electrode facing each other discretely in a pickling tank filled with a pickling solution so that the positive electrodes and the negative electrodes can be alternately arranged in a parallel with one another at distances, passing the metallic material through between the positive electrodes and the negative electrodes in the pairs in the pickling solution, thereby contacting the pickling solution with the metallic material, and applying a direct current to the metallic material by passing the current between the positive electrodes and the negative electrodes in the pairs.
(22) A process for removing scales and preventing scale formation on a metallic material, characterized by subjecting a metallic material to a pickling treatment by a pickling solution after the process according to any one of the foregoing items (1) to (16), followed by coiling.
(23) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (19) to (22), characterized in that the pickling solution is adjusted to a temperature of 50xc2x0 to 100xc2x0 C.
(24) A process for removing scales and preventing scale formation on a metallic material according to any one of the foregoing items (19) to (23), characterized in that the pickling solution is contacted with the metallic material at a relative speed of the pickling solution and the metallic material to one another of 0.1 to 300 m/s.
(25) An apparatus for removing scales and preventing scale formation on a metallic material, characterized by comprising a cooling apparatus that is comprising cooling headers and/or cooling nozzles for supplying cooling water and side guides for preventing leakage of cooling water from side edges, provided on the hot rolled metallic material at the outlet side of a hot rolling mill, and a direct current application to the metallic material through the supplied cooling water that is comprising pinch rolls provided on the outlet side of the hot rolling mill and acting as negative electrodes and being in electric contact with the metallic material, and rolls or apron guides provided behind the pinch rolls and acting as positive electrodes and being in non-electric contact with the metallic material through insulators.
(26) An apparatus for removing scales and preventing scale formation on a metallic material, characterized by comprising a cooling apparatus that is comprising cooling headers and/or cooling nozzles for supplying cooling water and side guides for preventing leakage of cooling water from side edges, provided on the hot rolled metallic material at the outlet side of a hot rolling mill, and a direct current application to the metallic material through the supplied cooling water that is comprising pinch rolls provided on the outlet side of the hot rolling mill and acting as positive electrodes and being in electric contact with the metallic material, and rolls or apron guides provided behind the pinch rolls and acting as negative electrodes and being in non-electric contact with the metallic material through insulators.
(27) An apparatus for removing scales and preventing scale formation on a metallic material, characterized by comprising a cooling apparatus that is comprising cooling headers and/or cooling nozzles for supplying cooling water and side guides for preventing leakage of cooling water from side edges, provided on the hot rolled metallic material at the outlet side of a hot rolling mill, and a direct current application to the metallic material with at least two of pairs each consisting of a positive electrode and a negative electrode facing each other being provided discretely in a water cooling tank filled with cooling water so that the positive electrodes and the negative electrodes can be alternately arranged in a parallel with one another, the metallic material being passed through between the positive electrodes and the negative electrodes in the pairs in the cooling water, thereby contacting the cooling water with the metallic material, and a direct current being applied to the metallic material by passing the current between the positive electrodes and the negative electrodes in the pairs.